Antifreeze removal

About 5 years ago I had in joist radiant heating installed and at the time the plumber put in antifreeze, due to a small cantilever section in the kitchen, it is really only 2 ft out by 6 ft wide.

I had access from below so I made sure the pipes were at ~ 2" from the top, bubble wrapped, fiberglass insulation and lastly 2" of rigid foam level with the bottom of the joist. I also plan to put either 1/2" or 1" foam across the bottom of the joists, then plywood, tyvek and cover that with siding.

The Furnace itself is 15 yrs old, hot water baseboard, pex tubing. I'm in Nova Scotia so not terribly cold, and I'm confident the pips will not freeze unless we have a long power outage. I have used a thermal or infrared heat sensor and the small cantilever section is 1 - 1.5 degrees colder than the inside floor, which is fine as there is a door and two windows in the area, so I'm comfortable there will be no issues.

I'd like to drain off the antifreeze and just use water, the radiators are copper with fins and the pex is connected to them, so no relief valve that I can see.

Can I just drain it ? I know where the drain valve is, and I expect I would shut the boiler down, turn off the water to the boiler and open the valve for the antifreeze fluid. when drained, would I just close the drain valve, open the water valve, let it pressurize and then turn on the heat to get the circulators going to purge any air out ?

and then repeat above to ensure all the antifreeze is out ? I also read to use drain the antifreeze, then add a tri phosphate solution 20% and pump it in the system run for 4 hours and drain to do a flush before refilling with water ?

Perhaps a picture of the boiler will help, I,m looking for instructions to properly drain the antifreeze from the hot water heating. I have a compressor, I've heard of some plumbers using that to push out water from the lines. Also is a rust inhibitor necessary?

I'd like to do the job correctly. From what I learned so far I think by letting the boiler cool completely, then turn off the zone feed valves, connect a hose to the drain on the right of the boiler, I think the lower left is just domestic hot water. then open one zone at a time to push the antifreeze out using the autofil lever, then close the zone release the autofil lever, and copy for the next zone. When done colse the drain, open the zones and fire up to boiler. sound reasonable ?